This invention relates to receiving apparatus for a message with one or more periodic signals simultaneously present in the message frequency band.
In the prior art an in-band signal is usually present in a message frequency band only when a message is not being received. If a periodic signal is to be received simultaneously with a message, the periodic signal is usually either transmitted outside the message frequency band, or at a low level which does not materially degrade the message quality, or by angle modulation of a carrier which is amplitude-modulated by the message. Each of these methods has unsatisfactory features in service. We do not know of any prior art relevant to this invention.